Problem: with a single `context.options` there is no way for user to
force which scope (local, global, both) is being temporarily set and
later restored.
Solution: replace single `options` context with `bo`, `go`, `wo`, and
`o`. Naming and implementation follows how options can be set directly
with `vim.*` (like `vim.bo`, etc.).
Options are set for possible target `win` or `buf` context.
07cc559cdf
